Process for making spinnerets for melt spinning



Jan. 21, 1958 w, 55 wo 2,820,374

PROCESS FOR MAKING SPINNERETSFOR MELT SPINNING Filed July 10, 1952 1.\VENTOR ,llzlem defiif ATTORNEYS ning high polymeric substances. of theinvention is to provide .a method for manufactur- United States PatentOPROCESS FOR MAKING SPINNERETS FOR MELT SPINNING 'Willem De Wolf, Arnhem,Netherlands, assignor, by mesne assignments, to American EnkaCorporation, Enka, N. C., a corporation of Delaware Application July 10,1952, Serial No. 298,042

Claims priority, application Netherlands November 23, 1949 4 Claims.(Cl. 76-107) This invention relates to av process for melt-spinning highpolymeric; substances and to the products obtained thereby, as well asto thespinnerets used in the spinning process and. to, the process formanufacturing these spinnerets. This application is acontinuation-in-part of my copending=U.-S. application SerialNo.192,969, filed "October 30, 1950.

One of ,the principal objects of the present invention is to provide anew and improved method for melt-spin- A still further object ingspinnerets useful in carrying out melt-spinning operations upon highpolymeric substances, as well as the .as it is being forced throughtheholes of the spinneret to form the threads or filaments are usually veryhigh in view of the relatively high viscosities of the molten highpolymeric material undergoing spinning. This pressure generally is ofthe order of at least atmospheres, and frequently rises as high as 40and even to 100 at- ..mospheres in certain instances.

In view of the solidification of the high polymeric substance as itundergoes cooling upon being squirted through the spinneret orificesinto the air, it is generally necessary that the. holes of the spinneretbe spaced a substantial distance from each other since otherwise thefreshly spun threads or fibers may give rise to difficulties due totheir sticking together during the cooling process. For-this purpose aspacing of atleast 3 to 5 mm. between the holes in the spinneret isgenerally necessary. It follows that if an artificial thread comprisinga rather large number of single fibers is to be spun in this fashion,the bottom of the spinneret in which the holes are present mayoftenreach a diameter of about.6 cm. or more.

In order to carry out melt-spinning operations under the circumstancesjust mentioned wherein such high internal pressures are encountered, itis necessary to manufacture the spinnerets from a particularly strongmaterial. As a rule -a special steel'is used for the spinneret material,which steel is not only strong but also completely resistant to themolten polymeric materialsyalthough base metals or alloys other thansteel which are also resistant under .thecircumstances mentioned mayalsobeused.. Q, a

In, the1conventional' wet-spinning process of' viscose uf t re. he. cuma es pre ai d ri g the spinning operation-are quite different. Theinternal-pressures in the spinnerets employed in the viscose process numand gold-palladium. or cheaper materials, some efforts have been made in10..

oture largely fromstainless steel or nickel by a procedure wh'erebyprecious metal inlays were fitted in theplaces iare inigeneral nothigher than a few atmospheres. Moreover, the holes in the spinneret maybe spaced as closely Has /2 mm. or less from each other. As aconsequence, ,it became obvious at a fairly early stage of developmentof the viscose art to employ spinnerets that were manu- -facturedcompletely from precious metals and alloys thereof such as platinum,platinum-iridium, gold-plati- In order to permit the use the, past tomanufacture spinnerets for viscose manufacwherethe holes were to beprovided. However, such spinnerets could not adequately fulfill therequirements in the; long run because the insertion of the preciousmetal inserts into the very thin bottom metal of the ,spinnerets at sucha short distance from each other was generally attended with too manydifiiculties, and it was soon found that the greatly increased costs ofmanufacture were not compensated for by the value of the material saved.Moreover, it was found that as a consequence of electrolytic action dueto the presence of metal couples, increased attack of the base metal ofthe spinneret occurred.

Surprisingly, the present applicant found that it was possible to employin high polymer melt-spinning operations a principle known broadly inwet-spinning, wherein precious metal inlays were inserted in base metalspinnerets. This was entirely contrary to any experience in in acorroding bath during the spinning operation. Moreover, the base metalis not attacked by molten polymers,

and while strong nitric acid is ordinarily employed in cleaning thesespinnerets, many types of stainless steel, such as V4a-steel, are knownto bevery well resistant to such acid. Finally, the fact thattheemployment of pressures that may range upwardly to as high asatmospheres in melt-spinning operations must be taken intoconsideration, as distinguished from the, at most, several atmospherespressures encountered in 'viscose spinning, excludes all those methodsknown to the viscose industry for inserting the precious metal inlays.

Moreover, in view of the cost and the hardness of the materialsrequired, it is not possible for practical reasons to manufacturemelt-spinning spinnerets entirely of precious metals.

Thus it is that contrary to what might have been expected by thoseskilled in the art, according to the present invention it has been foundthat if in a steel bottom plate of a melt-spinning spinneret inlays ofprecious metal are inserted and the necessary holes are then punchedtherein, the extrusion of the molten high polymeric substance throughthe holes thus formed in the precious metal inlays and the cold drawingof the resulting fibers can quite surprisingly be carried out far.better-and far more easily. It has been found that the thickness ofthethreads is far more even, so that with otherwise the samemeltspinning apparatus a much better quality of yarn is spun, andmoreover the cold drawing of these spun-threads, which operation isknown per se and which is one of the most important parts of the processfor manufacturing such threads, is found to take place far more easilybecause substantially less breakage due to breakage of single filamentsoccurs. Moreover, the resulting product isfar less fibrous in nature. 14

.Alternatively, and in accordance with another embodimerit oftheinvention, the precious metal inlays maybe first finished to the desiredsize and shape'completely, including punching or drilling the spinninghole in each conicity or taper.

inlay, after which the finished inlays are then placed in position inthe steel bottom plate of the spinneret.

When employing such a spinneret in melt-spinning operations, one mayemploy the procedure described in the copending U. S. application SerialNo. 115,773, filed September 14, 1949 by Theodoor Koch, now abandoned.

It was also found that when using nitric acid of sufficientconcentration to clean the spinnerets thus formed, no attack by electricpotential differences occurs therein, during the cleaning operation, sothat this reason which makes the application of precious metal inlays inwetspinning in the long run impossible, is not present here.

Although it is possible to insert the precious metal inlays in variousways in the base metal spinneret without departing from the spirit andprinciple of the invention, yet certain particularly preferableembodiments have been found, and these will be described hereinafterwith reference to Figures 1 and 2 of the accompanying drawing. Thus, itwas found particularly preferable that the thickness of the metal bottomplate of the spinneret be at least 3 mm., while the distance between thecenters of the holes in the spinneret should be preferably not less than3 mm. The holes in the "base metal spinneret, in which the gold or otherprecious metal inlays are inserted, preferably consist of two parts, theconicity or hole is such greater, and may be of the order of 60. .Theuse of stainless steel, for example V4a-steel, as the bottom material ofthe spinneret is :preferred.

Referring now to the accompanying drawing, Figure 1 shows on an enlargedscale a section of a part of the bottom of a steel spinneret, providedwith a precious metal inlay with a spinning hole;

Figure 2 is a section of the precious metal inlay per se I as it isready to be inserted into the bottom of the steel spinneret, and beforeit has had the spinning hole punched or drilled therein; and

Figure 3 is a section of a different form of the precious metal inlayper se, characterized by an internally streamlined configuration.

I Referring to Figure 1, there is shown a portion of a melt-spinningspinneret having a stainless steel bottom plate 1 having a thickness of5 mm. This spinneret has a plurality of holes 2 punched or otherwiseformed therein, of which one is shown in the drawing. On the inside ofthe spinneret the diameter 3-3 of this hole is 6.5 mm. The hole consistsof two parts of different The part of the conical hole which openstoward the inside of the spinneret has a depth of 3 mm., and is taperedwith a conicity of 60 from a. diameter of 6.5 mm. at 3-3 to a diameterof 2.7 mm. at 44. From 4-'4 to the outside -55 of the stainless steelplate 1 the hole 2 has a taper of 3 from a diameter of 2.7 mm. at 44 toa diameter of 2.5 mm. at 55. Although the conicity or taper of these twoportions of the hole in the bottom of the spinneret may be differentfrom the values just mentioned, it has been discovered that'for 'bestresults as regords the firm disposition of the precious metal inlay inthe bottom plate of the spinneret the conicity of the second part of thehole lying between '44 and 5-5 should be restricted and shouldpreferably "lie between 1 and 6. When stainless steel is employed as thebase. metal of the bottom plate 1, at 3 taper is found to give veryadvantageous results.

Thu-s, the hole in the stainless steel spinneret is characterized inthat it consists of two parts, the part lying nearer the outside face ofthe spinneret having a conicity remaining portion being of substantiallygreater conicity or taper.

It has been discovered that the precious metal inlay can be formed veryconveniently by cutting pieces of a length of 1.7 mm. from a preciousmetal wire, for ex ample one consisting of 70% gold and 30% platinum,with'a circular cross section having a diameter of 2.6 mm. Thereafterthis inlay is formed under very high pressure in a suitably adaptedpunching apparatus until it acquires a cup-shape, as indicated in Figure2. The cupshaped precious metal inlay there shown consists of a bodyportion 6 which on one end 77 has an outer diameter of 2.7 mm. and onthe other end 8-8 a diameter of 2.5 mm. In this piece a cup is formedwhich at the top '9--9 has a diameter of 1.8 'mm. and at the bottom10-10 a diameter of 0.8 mm., while the thickness of the precious metalat the bottom amounts to 0.45 mm. at the most, and preferably 0.40 mm.(between the planes 88 and 1010).

By means of a suitable stamp or press this cup-shaped precious metalinlay is now set in the conveniently adapted lower part of the hole 2previounsly formed in the steel bottom I of the spinneret. After all theholes in the steel spinneret bottom have been provided in this mannerwith inlays having cup-shaped recesses, the spinning holes '11 are thenformed in each of those inlays by drilling or one of the other'waysknown in the viscose industry and, if necessary, the spinneret ispolished on the outside. The spinneret is then ready for use inmeltspinning.

As an alternative procedure in manufacturing spinnerets useful inmelt-spinning according to the present invention, the present applicantalso'discovered that the precious metal inlays could be first completelyfinished, including the drilling or punching of the spinning orifice ineach inlay, .prior to assembling the inlays in the bottom plate of thebase metal spinneret.

According to this modification, the precious metal inlays are firstmanufactured as shown in Figure 2 to very close tolerances and then thespinning orifice 11 is "drilled or punched in each one while the inlayblank is held in a suitable die "or holding fixture to preventdeformation of the inlay during the perforating operation. Theperforated inlay pieces are then polished to remove tiny rough edges,after which they are inserted in the bottom plate of the base metalspinneret. When these manufacturing operations are carried out with careand due attention to maintaining all dimensions, both of the spinneretand of the inlay pieces, very exact, theprecious metal inlay pieces canbe fitted into the tapered holes provided in the base metal spinneret sothat the surfaces of the inlay pieces will be flush with the surface ofthe bottom plate of the spinneret, but without deformation of the tinyspinning hole.

As a still further modification of the present invention, it has alsobeen found that it is not necessary to give the precious metal inlaysthe particular cup shape shown more particularly at 910-109 of Figure 2.On the contrary, good results in melt-spinning are also obtained if theinternal walls of the precious metal inlays are given a streamlineshape, provided the thickness of the precious metal at the bottom ismaintained, as before, at about 0.45 mm. at the most, and preferablyabout 0.40 mm. This internally streamlined shape may be convenientlyimparted to the precious metal inlay pieces by forming them under veryheavy pressure in a suitably adapted punching apparatus as before, itbeing necessary only to employ an appropriately shaped male die toconfer the desired streamlining effect.

It is to be particularly understood that the precious metal inlay piecesmay be given the internally streamlined configuration as and'in themanner described above irrespectively of whether the spinning orifices11 are incor'p'orated therein before or after positioning them in seam 'l O thdbase tiie tal spinneret, in accordance with either of the methodsof manufacturealso described above.

vIt has been found that. in practice spinnerets made up as describedabove are completely resistant to the high pressures occuring during themelt-spinning process and that they give a product characterized byextraordinarily regular single filaments. r In order to indicate stillmore fully the nature of the present invention, thefollowing examples oftypical procedure are set forth, it being understood that thisdescription is presented by way of illustration only, and not aslimiting the scope of the invention.

Example 1 Polyamino-caproic amide having an intrinsic viscosity of 0.96was melted at a temperature of 256 C. in a meltspinning apparatus of aconstruction known per se. The molten polyamide was then forced througha filter and then by means of a measuring pump through a spinneretconstructed according to the present invention in which ten preciousmetal inlays formed as described above in connection with Figure 1, werepresent. In each of those precious metal inlays there was provided aspinning hole the mouth of which had a diameter of 250 microns. Theprecious metal inlays were located in the spinneret in such manner thatthe ten spinning holes were present on a circle with a diameter of 40mm.

The quantity of molten polyamide forced through the spinneret amountedto 11 grams per minute. The ten single filaments squirted out from thespinneret were collectively wound as one thread on a rotating spoollocated at a distance of about meters from the spinneret. This spool hada peripheral speed of 600 meters per minute, as a result of which anartificial thread of 165 deniers, consisting of ten single filaments,was formed. This thread was cold-drawn in accordance with conventionalcolddrawing practice to a four-fold length having a final thickness of45 deniers. On an average only one break occurred per 90 kilometers ofthread during this drawing operation.

Furthermore, it appeared from a microscopic examination of thecross-sections of this thread that each single filament had an almostexactly round cross-section. The differences in diameter of thecross-sections of these single filaments visible under the microscopewere measured. Practically all the variations lay between 2% and 4% fromthe largest diameter with a few exceptions which showed a deviation upto 5%.

In order to show the special advantages of the procedure according tothe present invention, attention is invited to the following comparativeexample.

Example 2 The procedure of Example 1 was repeated with the soleexception that instead of employing a stainless steel spinneret havingprecious metal inlays, a spinneret was employed having a stainless steelbottom plate having no precious inlays but in which the spinning holeswere formed directly in the stainless steel plate. On colddrawing thethreads spun by means of this spinneret, it was found that thereoccurred an average of 20 to 25 breaks per 90 kilometers. Moreover, themicroscopic examination carried out in the same way as in Example 1showed that, although the individual filaments were almost exactly roundjust as were those in Example 1, the differences in diameter were farlarger. Measurements showed differences in diameter that variedpractically between 8% and 12%, while a few differences in diameter ashigh as 20% were found.

Example 3 The melt-spinning procedure of Example 1 was re p rated exceptthat the spinneret was constructed by the Example 4 v The melt-spinningprocedure of Example 1 was repeated, except that the precious metalinlay pieces were internally streamlined as described above and asillustrated in Figure 3. The results were comparable in all respects tothose of Example 1.

Example 5 The melt-spinning procedure of Example 3 was repeated, exceptthat the precious metal inlay pieces were internally streamlined asillustrated in Figure 3. The results are comparable in all respects tothose of Example 3.

For applications where it is desired to make the bottom plate 1 of thespinneret unusually thick (e. g., 8-12 mm.) and/or to provide the bottomplate 1 with more than the usual number of spinning orifices, it issometimes advantageous to make the upper portion of the hole in thebottom plate 1 of cylindrical shape rather than conical shape, that isto say, in Figure 1 the distances 3--3 and 44 will be substantiallyequal, with the taper extendingv below the plane of 4-4.

While specific examples of preferred methods and ar-- ticles embodyingthe present invention have been recited above, it will be apparent thatmany changes and modifications may be made in the methods of procedureand in fabricating the articles herein described. It will therefore beunderstood that the examples cited and the par-- ticular methods andprocedures set forth are intended to be illustrative only and are notintended to limit the inven-- tion.

What is claimed is:

1. A process for manufacturing spinnerets for the high pressuremelt-spinning of high-polymeric substances comprising cutting aplurality of pieces from a cylindrical wire of precious metal, pressingthe pieces into cupshaped inlays having outer surfaces conforming tothat of a truncated cone and having a closed bottom end, setting theinlays into complementary holes formed in a steel spinneret plate havinga thickness of at least 3 mm. and thereafter forming a spinning hole inthe bottom end of each inlay.

2. A process as in claim 1 in which the inlays are set in holes in thesteel spinneret plate, each of said holes having two dilferent portionsof diiferent conicity, until the base of each of the inlays and the baseof the steel spinneret plate lie in substantially the same line.

3. A process for manufacturing spinnerets for the high pressuremelt-spinning of high-polymeric substances comprising cutting aplurality of pieces from a cylindrical wire of precious metal, pressingthe pieces into cupshaped inlays having outer surfaces conforming tothat of a truncated cone and having a closed bottom end, forming aspinning hole in the bottom end of each inlay and thereafter setting theinlays into complementary holes formed in a steel spinneret plate havinga thickness of at least 3 mm.

4. A process as in claim 3 in which the inlays are set in holes in thesteel spinneret plate, each of said holes having two difierent portionsof difierent conicity, until the base of each of the inlays and the baseof the steel spinneret plate lie in substantially the same line.

(References on following page) References Cited in the file of thispatent 2,232,417 Unckel '1 Feb. 18, 1941 UNITED STATES PATENTS 2,376,742Wempe May 22, 1945 1,420,224 Simons -1 June 20, 1922 V FOREIGN PATENTS1,597,928 imons Aug- 31, 1926 5 141,840 Austria Ian. 15 1935 1,604,216Brainin Oct. 26, 1926 1,654,936 Iqncs Jan. 3 1928 OTHER REFERENCES Y1,672,644" Hoffmann et a1 Ju'fie' 5, 1928 I S N 97, Wempe pubhshed p1,752,689 Ohlson Apr. 1, 1930 3- 2,051,663 Werth Aug, 18, 1936 10 Ser.No- 349,256, Aschenbrenner et al. (A. P. 0.), Apr.

2,058,032 Murphy Oct. 20, 1936 27,1943

